JPS6134426A - Filter device of octave analyzer - Google Patents

Abstract

PURPOSE:To make it possible to change the number of divisions for every octave, by determining the width of a frequency, which is to be analyzed by a bandpass filter, passing the Nth input signal, and forming the (N-1)th input signal and thereafter by a low-pass filter. CONSTITUTION:An input signal Si is converted into a digital signal through a low-pass filter 11, and an A/D converter 12. A bandpass filter 13 divides an octave signal, which is selected by an octave selecting command sc and a dividing command dc from a sequence controller 17 and performs bandpass opration. Of the input signals, the (N-1)th octave signal is made to be the upper limit. This signal is made to pass a low-pass filter 15. The signal is stored in a RAM 16 and sent to the filter 13. At this time, a ROM14 imparts the number, by which the (N-1)th octave is to be divided, to the filter 13. Thus the number of divisions for every octave can be varied.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Application of the Invention] The present invention relates to a filter device for a two-octave analyzer.

[Technical background of the invention]

For example, when implementing noise prevention measures, it is necessary to measure noise under various conditions, and it is also necessary to consider the effects of noise prevention, such as sound insulation effects, sound absorption effects, and novelty 2 effects.

In each of these cases, the measurement signal has a very complex waveform, so generally the input signal sound is analyzed and divided into elementary wavenumber components, each of which is processed, and finally synthesized again. are being expelled.

Octave analyzers and 1/3 octave analyzers are used for the purpose of this type of frequency analysis.

An octave analyzer is a filter whose passband is in an octave relationship (for example, 45-90Hz, 90-180Hz).
Roux 180-360, 360-720.720-14
40 outputs, etc.) to perform frequency analysis. Further, the bad octave analyzer performs frequency analysis by dividing the octave into three frequency bands at a predetermined ratio, and has three times the resolution of the octave analyzer.

By the way, in actual frequency analysis, it is necessary to change the resolution for each frequency band, such as in some frequency bands it is necessary to analyze every octave, and in other frequency bands it is necessary to analyze every 1/3 octave. There are cases. Also,
There are cases where it is desired to change the resolution for each measurement.

However, the frequency band that is the unit of analysis for most conventional analyzers is either 1 octave or 1/3 octave, and it is not possible to change the resolution depending on the frequency band being measured. Ta.

[Purpose of the invention]

This invention was made based on the above-mentioned circumstances, and the frequency band that is the unit of analysis can be set to any 1/r'I.
Provided is a filter device for a two-octave analyzer that can be used as an octave and in which n (-1, 2, 3, 4,...) can be arbitrarily set to change the resolution in each frequency band. The purpose is to

[Summary of the invention]

To achieve this objective, the present invention comprises a digital bandpass filter and a digital lowpass filter, and determines the frequency width (1/r+octave) to be analyzed by changing the coefficients of the digital bandpass filter. The input signal of the N-th octave is passed through the digital band-pass filter, and the input signal is passed around the low-pass filter, thereby forming input signals of the N-1th and subsequent octaves. In this case, it is not necessary to change the coefficients of the bandpass filter unless the frequency width to be analyzed is changed.

[Embodiments of the invention]

Hereinafter, the present invention will be described in detail with reference to the accompanying drawings.

In the following description, it is assumed that signals (referred to as octave signals) consisting of octaves from the first to the Nth (N is a positive integer) starting from the lowest frequency are analyzed.

FIG. 1 is a system diagram showing an embodiment of the present invention.

According to the figure, a low-pass filter 11, an AD converter 12, a digital band-pass filter 13, a first memo 4, a digital low-pass filter 15, a second memory 16, and a sequence control section 17 are shown.

The low-pass filter 11 is for removing frequencies other than the required frequency band from the input signal and preventing aliasing in subsequent sampling. Therefore, it is sufficient that an octave signal including the highest frequency among the frequencies of the signal to be analyzed can be passed, and the Nth octave signal in FIG. 2 is set as the upper limit for passing. In noise analysis, the cutoff frequency of the low-pass filter 11 is set to 20,000 Hz, for example.

The AD converter 12 digitizes an analog input signal for subsequent processing.

The digital band pass filter 13 is provided with predetermined coefficients from the ROM 14, which is a first memory, to filter n frequency bands (n is A positive integer) is divided into small bands to provide bandpass characteristics. Such division into n small bands is called 1/rI octave analysis.

At this time, this octave signal is sampled at a frequency of fs/211.

Here, as shown in FIG. 3, the sampling frequency is set to fs (fS>2fN+nax) with respect to the upper cutoff frequency fN max of the Nth octave signal.

Next, set the sampling frequency fs to the upper cutoff frequency fN-1mmx of the N-1st octave signal.
/2, the relationship fs/2>fN-1rnax, that is, the sampling theorem is satisfied, and it is known that this holds true for all octave signals.

Therefore, the X-th octave signal among the N octave signals can be sampled at the frequency fs/2N-''.In addition, at this time, the number n by which the frequency band forming each octave signal is divided into subbands is not changed. As far as possible, the coefficients from the RAM 14 applied to the bandpass filter 13 do not need to be changed for all octaves.

The digital low-pass filter 15 uses a signal whose upper limit is the X-th octave signal as an input signal, forms a signal whose upper limit is an octave signal before the 13
It is prepared for processing in That is, when sampling the N-1st and subsequent octave signals with the band-pass filter 13, the low-pass filter 15 prevents a return signal due to the sampling link from appearing within each octave band.

Therefore, the coefficients of this low-pass filter 15 are changed each time depending on which octave is to be processed. This coefficient is given from the sequence control section 17.

The second memory 16 temporarily stores the output of the low-pass filter 15 and sends it to the band-pass filter 13 according to a command from the sequence control unit 17.
recirculate to.

The sequence control unit 17 determines the timing of the operations of the band pass filter 13, the low pass filter 15, and the RAM 16, which is a second memory, and also controls the operation of the band pass filter 1
The sampling frequency fS/2N-1 of 3 is specified, and the coefficients of the ROM 14 are specified.

In other words, specify the sampling frequency fs/2 and
After the band-pass filter 13 processes the second octave signal, a signal whose upper limit is any octave signal from X-1 to Specify a sampling frequency corresponding to an arbitrary octave signal, and specify the desired number n of subbands into which this arbitrary octave signal is to be divided.
Specify the first memo January 4th.

Next, the operation of this embodiment will be explained.

The input signal S1 is filtered by the low-pass filter 11, and contains only the Nth to first octave signals, N,11
Octave signals above the 1st are cut off (Figure 2)
.

Such an output signal of the low-pass filter 11 is converted into a digital signal by the AD converter 12N-x, and is input to the digital band-pass filter 13 and the high-frequency low-pass filter 15.

The bandpass filter 13 operates according to the octave selection command sc and division command dc from the sequence control unit 17.
The number of octave signals to be subdivided and bandpassed is specified.

Here, consider a case where the Nth octave signal is divided into three, the N-1st octave signal is divided into one, and the Xth (x N-2) octave signal is divided into one. If this case is expressed in analog form, it will be as shown in FIG. this is,
Octave signal and h-octave analysis are mixed.

Currently, a signal whose upper limit is the Nth octave signal is input to the bandpass filter 13, and a command is given to divide the Nth octave signal into three and bandpass the divided signal.

Therefore, at the timing when a signal whose upper limit is the Nth octave signal is input to the bandpass filter 13, the RO
M14 gives a coefficient for dividing the Nth octave signal into three and bandpassing it, performs sampling at frequency fs, and performs analysis.

At this time, the signal whose upper limit is the Nth octave signal is also input to the digital low-pass filter 15.

The low-pass filter 15 is instructed to set the upper limit to the N-1st and and pass the signal.

Therefore, the RAM 16 stores a signal whose upper limit is the N-1st octave signal.

The signal whose upper limit is the N-1st octave signal stored in the RAM 16 is input to the bandpass filter 13 and the hero bass filter 15 at the timing when the bandpass filter 13 finishes processing the Nth octave signal. .

Here, the ROM 14 stores the N-1st octave signal as 1
Give the coefficient for bandpassing the division (that is, the N-1th octave signal as it is), and set the frequency fs/
Perform sampling and analysis with 2N-x.

On the other hand, the signal whose upper limit is the N-1st octave signal input to the low-pass filter 15 is given a coefficient by the sequence control unit 17 so as to be low-passed with the X-th octave signal as the upper limit, and the signal is passed. .

Therefore, the RAM 16 stores a signal whose upper limit is the X-th octave signal.

The signal whose upper limit is the X-th octave signal stored in the RAM 16 is input to the band-pass filter 13 and the low-pass filter 15 at the timing when the band-pass filter 13 finishes processing the N-1-th octave signal.

Here, the ROM 14 divides the X-th octave signal into one (that is, leaves the X-th octave signal as it is).
Coefficients for bandpassing are given, but since the N-1st octave signal is also divided into 1, there is no need to change the coefficients. Sampling is performed at a frequency fS/2N-'' to perform analysis.

Since no further analysis is commanded, the low-pass filter 15 sends no further output. Alternatively, the input of the X-th octave signal to the low-pass filter 15 may be prevented.

As can be seen from the above explanation, by assigning a predetermined coefficient to the low-pass filter 15, a signal whose upper limit is a desired octave signal can be obtained, and this signal can be input to the band-pass filter 13. Predetermined □ from ROM14
The input signal can be analyzed by dividing the octave signal into arbitrary small bands by adding coefficients.

〔Effect of the invention〕

By configuring as described above, this invention can divide an arbitrary octave signal into arbitrary small bands for analysis, and can change and mix the number of divisions for each octave signal. A filter device for an octave analyzer can be provided.

[Brief explanation of drawings]

FIG. 1 is a system diagram of an embodiment of the present invention, and FIGS. 2 to 4 are diagrams for explaining the operation of the embodiment of FIG. 1. 11...Low pass filter, 12...AD converter, 13...Digital band pass filter, 14...
... first memory, 15 ... digital low-pass filter, 16 ... second memory, 17 ... sequence control section.

Claims (1)

[Claims] Out of the input signals divided into N octaves (N is a positive integer), the x-th (x is a positive integer, N≧x) octave signal is divided into frequency fs/2^N^-^ a digital bandpass filter that samples at x and divides a frequency band forming the Nth octave into n small bands (n is a positive integer) to give bandpass characteristics; a first memory storing coefficients for imparting characteristics; and a digital low-pass filter that receives a signal whose upper limit is the x-th octave signal as an input signal and forms a signal whose upper limit is the x-1-th octave signal. , a second filter to recirculate the output of this low-pass filter.
a memory, and after the sampling frequency is specified and the Nth octave signal is processed by the bandpass filter, a signal whose upper limit is an arbitrary octave signal from the x-1th onwards is transferred from the second memory to the bandpass filter. Sequence control means for specifying the sampling frequency corresponding to the arbitrary octave signal sent to the filter, and specifying in the first memory the desired number n of subbands into which the arbitrary octave signal is to be divided. The filter device of the octave analyzer consists of: